Despite their importance in a balanced ecosystem, insects are often a source of discomfort, disease and property damage. Because of their extensive impact on humans, many solutions have been proposed over the years to control the population of insects within our habitat. These solutions can be broadly grouped in two main categories according to their mechanism of action; chemical and physical.
Chemical approaches for insect control target the biochemistry of the specific insect target group. A substance is used to destroy (insecticide), or interfere with the behavior of the target organism in some stage of its lifecycle, e.g. repellents. Despite their recognized effectiveness in controlling insect populations, chemical approaches produce undesirable side-effects that range from unpleasant odours to human poisoning.
DEET (N, N-Diethyl-meta-toluamide), the most common active ingredient in insect repellents, is an example of an effective chemical substance for insect control that is nonetheless a harmful substance to humans. DEET is often sold and used in spray or lotion in concentrations up to 100%. The potential health effects of the product are eye, throat and skin irritation as well as central nervous system effects if inhaled. The effect of DEET in inhibiting the activity of the central nervous system enzyme acetylcholinesterase was in fact observed in both insects and mammals. Health concerns over the use of DEET substance triggered the Canadian federal health agency to prohibit insect repellents with concentrations above 30% and discourage the use of the product in the vicinity of children younger than 2 years old.
Icaridin (a.k.a. picaridin) is a largely colorless and odorless substance—also used in insect repellent lotions to be applied on the skin—whose efficacy is comparable to that of DEET. The World Health Organization (WHO) classifies icaridin as a slightly hazardous substance whose risks to people, animals and environment are acceptable. The substance is nevertheless slightly toxic to humans and is absorbed through the skin or via inhalation and its health effects will depend on concentration and frequency of exposure.
Allethrihns are synthetic compounds used in insecticides that present low toxicity to humans and are used in domestic products. The WHO classifies it as a slightly hazardous substance and conditions its safety to appropriate use. It also reports it to be highly toxic to fish and honey-bees.
Lambda-cyhalothrin is an organic compound used in long-lasting insecticides for backyards that is also hazardous to human health and generates a strong and unpleasant smell. Citronella oil is a natural insect repellent obtained from the leaves of lemongrass. The United States Environmental Protection Agency considers citronella oil to be of low acute toxicity that poses minimal risk to the ecosystem. The substance is rather innocuous to humans upon inhalation but displays a strong smell that is not always appreciated. Citronella oils are often dispersed in the air to repel mosquitos by burning an impregnated candle.
Chemical substances with repellent properties are often dispersed in the environment in the format of incense, such as mosquito-coils. However, burning incense creates a fire hazard besides producing a large amount of solid particles and gases in the air. In view of the undesirable by-products generated by mosquito coils, exposure to their smoke can pose significant acute and chronic health risks.
Electrical devices are also often used to disperse chemical substances in the environment. Dispersion is achieved either by heating or spraying (misting) the substance in a controlled manner. This approach does not generate noxious combustion by-products as mosquito coils do, but they are still based on the diffusion of hazardous substances into the environment.
Physical approaches for insect control rely on the use of mechanical barriers or different forms of energy e.g. sound and light, that can affect behavior.
Mechanical barriers normally assume the form of screens or nets placed on windows, doors or around beds. These screens allow for the circulation of air, but the pores are small enough to prevent the entrance of insects in a certain space. Although effective if used correctly, this approach does not address the problem of insects that are already inside the target area.
Sound is used in a range of products intended to repel insects. However the effectiveness of available devices has been strongly questioned. A review by the Cochrane Collaboration, an international entity that supports evidence-based healthcare, concluded from the results of 10 field studies that such devices had no effect on the number of insects caught from the bare body parts of humans.
This invention relates to the use of light for insect control. Various species of insects found in people's residences are either attracted or repelled by light at some stage of their lifecycle. Amongst the insects that show attraction to light many display preference to light sources with more energy in the short wavelengths i.e. blue and ultraviolet. This phenomenon is applied in several devices used as insect traps: blue light sources lure insects to a space where they are either electrocuted by touching filaments (bug zappers) or fumigated.
Effective light traps, however, are known to disturb people in a perceptible way, either visually, audibly or aromatically. Visual disturbance is caused because the light source used to lure must be noticeable so as to attract the insects in the target area. This spatial requirement limits the choice of positioning and dimming the light sources. Audible or aromatic disturbance is caused because traps must be collocated with the light source which implies killing the insects in a nearby visible location. As electrocution generates unnerving noise and smell, and fumigation relies on hazardous substances, effective light traps are not much favored in inhabited spaces. Such traps are mostly relegated to outdoor areas and studies of insect populations.
Insects perceive electromagnetic radiation over a wide range of wavelengths in the visible and near-visible spectra. The photoreceptor cells within their eyes contain different rhodopsins, i.e. visual pigments that react to light of specific wavelengths.
Bichromatic insects express two types of rhodopsins, one with maximum absorption in the UV range and another with maximum absorption in the green range. Some insects are trichromatic and have a third pigment whose absorption peaks at blue wavelengths. Yet another group of insects, particularly some species of Lepidoptera, are tetrachromatic and carry an additional pigment with peak absorption in the red wavelength region.
The perception of light has been observed to play a role in navigation, foraging and meeting sexual partners for both winged and terrestrial insects. This adaptive behavior based on the ability to perceive nuances in environmental lighting conditions, e.g. intensity, polarization and spectral distribution, seems crucial for survival as it maximizes the chances of finding food and mates while avoiding predators.
Many species of insects display phototaxis, i.e. a disposition to move in response to light, either towards or away from the light source. Negative phototaxis facilitates locating shelters to avoid predators while positive phototaxis intermediates the flight response in many flying insects.
Insect phototaxis has practical consequences to their ecology in a world where artificial light increasingly dominates the skyline during nighttime. Artificial light often perverts the natural phototactic behavior of insects driving them away from their habitat. A study in a German city of 240,000 inhabitants estimated that about 360 million insects die per season attracted to street lamps. Insect mortality may negatively impact entire ecosystems through the destabilization of food chains. Besides increasing mortality, the movement of insects to urban environments may bring discomfort, destruction and diseases to humans. A study in Mexico showed that houses closer to public street lights were more likely to be infested with Triatoma dimidiate, one of the primary vectors of Chagas disease.
From both the ecological and human wellness perspective there are thus incentives for keeping certain insects away from cities and buildings. Preventing attraction can be accomplished by choosing light sources displaying a low positive phototactic footprint. Conversely, driving insects away from buildings can be facilitated by exploiting negative phototactic behavior. Indeed, many establishments in the food industry rely on insect traps with UV enriched light to lure insects away from the kitchen or storage areas. The negative phototaxis of certain insect species, e.g. cockroaches, can also be leveraged to achieve similar effects.
In agriculture, greenhouses are spaces where temperature, humidity and lighting conditions can be controlled for optimizing yields. The lighting conditions in greenhouses have been increasingly used as a tool for integrated pest management. Light-based methods for reducing the presence of harmful insects include using phototactic behavior for luring and trapping insects, creating competing visual stimuli to disrupt the navigation process of pests; adding radiation with harmful or inhibitory wavelengths to kill or supress pest populations; providing time cues to influence daily rhythm; and the use of plastic filters to remove UV from daylight.
As an inalienable part of the food chain, insects are a source of nutrition to a wide range of animal species, including livestock and humans. The Food and Agriculture Organization of the United Nations (FAO) published a paper in 2013 advocating insects as a viable source of food security in the face of steep population growth. Indeed, it is estimated that insects form part of the traditional diets of at least 2 billion people. More than 1 900 species have been reportedly used as food. Insects also play a beneficial role as pollinators in plant reproduction, as agents of waste bioconversion, as biocontrol for harmful pest species, and as producers of honey and silk. Farming insects for economical active purposes is thus an economically attractive activity in which lighting plays an important role for supporting mating, oviposition, eclosion, and growth rate of insects.
Insect behavior is a dynamic process in which environmental conditions interact with endogenous states to elicit specific responses. Since natural environmental conditions usually change in a predictable periodic manner, insects have evolved mechanisms to anticipate such changes and adapt accordingly. As a consequence, the manifested behavior of insects is rich in cycles that closely match diurnal or seasonal patterns.
Due to the need of specialization in a complex ecosystem, different species of insects have differentiated response to environmental stimuli: some species begin to swarm in early spring, while others in midsummer; some insects display strong positive phototaxis to the green light while others do not. Not only do insect responses to environmental stimuli vary between species, but they often change within the lifecycle. Some species of termites for instance are attracted to light during their winged phase but are repelled by it after losing their wings.
This variability of insect response to external conditions within and between species means that the insect population in a given area is constantly changing over time as insects are triggered to mate, migrate or look for shelter. A changing population allied to the differentiated response of each species represents a challenge for creating solutions to influencing insect behavior with broad range effectiveness over time. In the particular case of lighting solutions for example, if the intended effect is to reduce the attraction of insects to the illuminated area, the efficacy may be high during a certain season when the insect population is primarily comprised of specimens who reject the light, but poor in another season when other specimens who do not reject the light are present.